The present invention relates to a drum plotter installed on a terminal device connected to a computer for drawing characters, figures, graphs and other patterns in multiple colors, and more particularly to a pen switching mechanism in such a drum plotter.
There have recently been developed plotters having a pen with water-base or oil-base ink movable back and forth across the width of a sheet of print paper or in a direction normal to the direction in which the sheet of print paper is fed along. Characters, figures and the like can be drawn on the paper by controlling the movement of the print paper and the pen in X and Y directions. To enable the plotter of this type to draw characters and figures in multiple colors, a plurality of pens with differently colored inks are supported on a rotary pen holder rotatable to move a pen with a desired color into a writing position. One known mechanism for rotating the pen holder to switch the pens has a fixed lever for pushing the pen holder to rotate the same by utilizing the force with which the pen holder is moved across the sheet of print paper. This prior mechanism however is disadvantageous in that it is time-consuming to switch the pens since the pen holder needs to be moved back to the fixed lever each time a desired pen is to be selected.
The plotter also has a hammer for pressing the pen selectively against the sheet of print paper. The hammer is driven by a solenoid fixed in a position different from a pen carriage supporting the pens and energizable to actuate the hammer through a shaft that guides the pen carriage in its movment. With this arrangement, however, the hammer actuating power is transferred through the shaft, and hence operating errors are accumulated to the point where the movement of the pens driven by the hammer cannot be adjusted easily.
The drum plotter has pens supported horizontally in confronting relation to a platen. Since there is a tendency for no ink to come out of the pens when recording is just started, it is necessary that something be drawn on the paper on a trial basis to see if the ink flows out properly. This process delays the starting of desired recording, and produces a useless length of print paper.